For decades, the traditional practice in animal testing has been standardization, but a study involving Purdue University has shown that adding as few as two controlled environmental variables to preclinical mice tests can greatly reduce costly false positives, the number of animals needed for testing and the cost of pharmaceutical trials. Source: Purdue University - Discipline: Research

"Human drug trials get around this problem by deliberately including variability in the experiment in a controlled manner so that the effect of a drug can be tested across a variable human population," Garner said.
"Overall, the differences between experiments are much, much greater in the standardized setups than in the ones where we deliberately varied the environment as if the experiment was a human drug trial," said Garner, whose results were published in the current issue of the journal Nature Methods. "In fact, the traditional standardized experiments generally disagreed with each other, while the experiments designed like a human drug trial generally agreed with each other."